Dithiocarbamic acid derivatives



. rubber.

Patented Oct. 3, 1944 DITHIOCAR-BAMIC AGTLD DERIVATIVES Joy G. Lichty,Stow, Ohio, assignor to Wingfoot Corporation, Akron, Ohio, a corporationof Delaware No Drawing. Original a Serial No. 81,485. Di

pplication May 23, 1936, vlded and this application February 21, 1941,Serial No. 379,993

13 Claims. (Cl. 269345) This invention relates to the vulcanization ofMore particularly, it relates to a new class of accelerators for thevulcanization of rubber, namely, the formaldehyde reaction products ofdithiocarbamic acids.

The invention has for objects the provision and preparation of a newclass of vulcanization accelerators, their use in rubber and rubbervulcanized in their presence. Other objects and advantages will becomeapparent as the descriptionv of the invention proceeds.

Heretofore various dithiocarbamates have been used in the vulcanizationof rubber. Among them are the bivalent metallic salts and substitutedammonium salts of dialkyl dithiocarbamic acids and the 2-4-dinitrophenyl esters of dialkyl dithiocarbamic acids. Bruni has also vulcanizedrubber in the presence of the formaldehyde reaction products of ammoniumsalts of dithiocarbamic acids .as disclosed in United States PatentsNos. 1,886,636 and 1,892,719.

This invention resides in the discovery that when formaldehyde isreacted with a dithio carbamic acid, new compositions which areexcellent accelerators are obtained. Since dithiocarbamic acidsgenerally exist only in solution and then, only for a short time, theproducts of the invention are preferably prepared by adding anacidifying agent to a solution or liquid dispersion containingformaldehyde and a dithiocarbamate. The dithiocarbamate should be onewhich does not react with formaldehyde and which will form the free acidupon acidulation. The metallic salts, particularly the alkali metal andalkaline earth metal salts, are quite satisfactory. The zinc and otherbivalent metal salts may also be used, however. The reaction is carriedout in a liquid medium of which a mutual solvent for the reactants, suchas water, alcohol and acetone, is preferred. It has been found desirableto conduct the reaction in the coldgenerally below a temperature ofabout 15 C.- although room and higher temperatures may be used, too. Atemperature at which the free dithiocarbamic acid will not decomposebefore its reaction with the formaldehyde is preferable, of course. Sucha temperature need not be a low one.

The reacting materials appear to react in molar proportions and suchproportions are usually employed in the practice of the invention,although an excess of formaldehyde is often desirable. Although themechanism of the reaction and the constitution of the final products arenot known definitely, it is believed that the acidifying agent firstreacts with the dithiocarbamate to release at least momentarily the freedithiocarbamic acid which then reacts with the formaldehyde to form amethylol ester of the dithiocarbamic acid. Consequently, at least a molof acidifying agent per mol of dithiocarbamate should be used. Also,there should be employed at least one mol of formaldehyde for eachdithio carboxy radical present in the dithiocarbamate. It will beunderstood that the invention is not to be limited by the varioustheories expressed herein and that it is not known just what happens butthat in any event new compositions of matter which are excellentaccelerators of rubber vulcanization are formed. In View of theuncertainties of the constitution of the products, they will be referredto herein as reaction products.

Example 1 Further illustrating the practice of the invention is thereaction of formaldehyde with dimethyl dithiocarbamic acid. It may becarried out as follows:

A mixture of 314.4 grams of an aqueous solution containing 0.4.- mol ofsodium dimethyl dithiocarbamate and grams of 36% formaldehyde wasstirred vigorously and maintained at a temperature below 10 C. duringthe addition of 300 grams of 5% H01. A liquid separated out and wasremoved by means of a separatory funnel. The remaining material wasallowed to stand in the open over night and was then dried in a vacuumdesiccator over H2SO4. The resulting amber viscous liquid weighing 29.2grams possessed a specific gravity .at 26 C. of 1.14. Its chemicalnature is not known definitely. Formaldehyde may, however, react withdimethyl dithiocarbamic acid according to the following equation:

(CH3) 2NCSSH+CH2O CH3) zNCSSCHzOH The analysis of the product approachesthe calculated values assuming this formula.

36.30, 36.10 Calc. for

The-analysis is not in particularly close agreement with the calculatedvalues but offers some evidence of the nature of the reaction.

Example 2 The product of dibenzyl dithiocarbamic acid and formaldehydemay be prepared as follows:

One mol of dibenzyl amine was added to 500 cc. of ice water and l igrams of 90% sodium hydroxide were then added. When the caustic had goneinto solution, 80 grams of carbon bisulfide were added in portions. Inabout fifteen minutes, a homogeneous solution was obtained. To thissolution were added 80 grams of 36% formaldehyde solution. A slightchange in the depth of the yellow color of the solution was observed.The beaker containing the solution was then equipped with mechanicalstirring and the acid was added slowly and in portions. The acid wasmade up by adding 100 grams of 36% hydrochloric acid to ice and watermaking up 500 cc. of the dilute acid. When the acid was first added adark oil separated out. This was removed and the addition of acid wascontinued. A bulky, white crystalline precipitate was formed. The whitecrystalline precipitate was filtered off, washed with cold water anddried, leaving a white, crystalline solid. This material was soluble inpractically all organic solvents with the exception of gasoline (B. P.40-140 C.) and petroleum ether. It was found that the material could berecrystallized by dissolving in ether, then adding gasoline or petroleumether and allowing to evaporate slowly. These crystals melted at 98 C.Further recrystallization gave a product that also melted at 98 (3.,showing a pure product. It is known that methylene bis dibenzylaminemelts according to the literature at 97 C. Accordingly, a quantity ofmethylene bis dibenzylamine was prepared and a mixed melting pointobtained which showed that the two materials were not the same (mixedmelting point below 80 C.). A qualitative analysis for sulfur showedthat the new product contained sulfur which clearly and conclusivelyestablished the non-identity of the two products.

To test whether this material melting at 98 C. was the carbon bisulfideaddition product of methylene bis dibenzylamine, some of this mate rialwas prepared by dissolving some pure methylene bis clibenzylamine incarbon bisulfide and allowed to stand several days during which theexcess solvent was allowed to evaporate slowly. A solid was obtainedwhich was found to be quite soluble in organic solvents. By dissolvingin ether and adding twice the volume of petroleum ether, crystals weredeposited on cooling. These, however, melted at 73 0. instead of 98 C. Arecrystallization gave a product with the same melting point (73). It isquite clear that the product obtained according to the practice of thepresent invention is not the addition product of carbon bisulfide andmethylene bis dibenzylamine.

Analysis showed this 98 material to contain 5.08% nitrogen and 20.85%sulfur. These figures agree quite closely with the calculated values of4.62% and 21.12%, obtained by assuming the formula to be When the sodiumsalts of ditetrahydro alpha furfuryl dithiocarbamate and di-n-amyldithiocarbamate were reacted with formaldehyde in the presence of anacid as in the preceding examples, the products obtained were viscous,light yellow oils which resisted efforts to crystallize them. However,these oily products are suitable for incorporation into rubber andfunction excellently as accelerators.

By procedures similar to the above any other dithiocarbamate may bereacted with formaldehyde. If desired, other salts, such as the zinc,potassium, calcium, etc., dithiocarbamates, may be used in place of thesodium salt. Also, any other dithiocarbamate which does not react withthe formaldehyde and which will form the free acid upon acidulation maybe employed. In some cases, from the standpoint of solubility, it may bepreferable to dissolve the dithiocarbamate in a water miscible solventsuch as acetone or alcohol instead of water.

Illustrative of other dithiocarbamates which may be employed in thepractice of the invention are those prepared from the dialkyl aminessuch as methyl ethyl amine, diethyl amine, di-npropyl amine,di-iso-propyl amine, ethyl isopropyl amine, di-n-butyl amine, di-isoamyl amine, methyl n-propyl amine, methyl isobutyl amine, diheptyl amineand methyl heptyl amine. Others are those prepared from the secondaryalicyclic amines such as dicyclohexyl amine, N-ethyl cyclohexyl amine,N-methyl cyclohexyl amine, tetrahydro alpha furfuryl cyclohexyl amine,N- butyl cyclohexyl amine, the di-hexahydro oand p-toluidines, thedi(hexahydro oand p-phenetidyl) amines, the di-(hexahydro oand p-anisyl)amines, etc. Still other dithiocarbamates are those prepared fromN-butyl tetrahydro alpha furfuryl amine, di-(alpha furfuryl) amine, di-(beta phenethyl) amine, sym. dibutyl ethylene diamine, sym. dicyclohexylethylene diamine, methyl aniline, ethyl aniline, cyclohexyl aniline,etc. The preferred dithiocarbamates are those prepared from secondaryamines containing at least one aliphatic, including cycloaliphatic,radical or a substituted aliphatic radical as is the case in the benzyl,beta phenethyl, tetrahydro furfuryl and furfuryl radicals. Thus, thepreferred class includes the dithiocarbamates in which the th iocarbamylradical contains the amino radical in which R is a radical selected fromthe group consisting of alkyl, alicyclic, tetrahydrofurfuryl, furfuryland aralkyl groups and R is a radical selected from the group consistingof alkyl, alicyclic, tetrahydrofurfuryl, furfuryl, aralkyl and arylgroups. Particularly preferred are the dialkyl dithiocarbamates.

Also, it is not intended that the invention be limited to thehydrochloric acid of the examples. Any other acidulating agent whichwill serve to liberate the free dithiocarbamic acid from thedithiocarbamate may be used. These other materials may be inorganic suchas sulphuric and phosphoric acids, sodium bisulfate, potassiumdihydrogen phosphate, etc. or organic such as acetic, formic andpropionic acids. Also, the acidulating agent should be low in oxidizingproperties so that there will be little or no tendencies to oxidize thedithiocarbamate to a thiuram disulfide.

It will be understood that in place of ordinary formaldehyde,formaldehyde polymers and the like which yield formaldehyde during thereaction may be used.

The products of the invention may be employed as accelerators in mostrubber formulae.

The following is one specificformula in which they have been found bytest to yield excellent results:

Parts by Weight Extracted pale crepe rubber 100 Zinc oxide Sulfur 3Stearic acid 1.5 Accelerator 0.5

Representative products of the invention were incorporated into rubberin accordance with the above formula. Samples were then cured andtested. The following results were obtained:

PRODUCT OF DITETRAHYDRO ALPHA FURFURYL DITHIOCARBAMIC ACID FORMALDEHYDEThese data demonstrate that the products of the invention are powerfulaccelerators, giving high tensile strengths in a very short cure.

This application is a division of copending application Serial No.81,485, filed May 23, 1936, now Patent No. 2,238,331, April 15, 1941.

Although only the preferred forms of the invention have been describedin detail, it will be apparent to those skilled in the art that variousmodifications may be made therein Without departing from the spirit ofthe invention or the scope of the appended claims in which it isintended to cover all features of patentable novelty inherent in theinvention.

I claim:

1. As a new composition of matter, a product obtained by reactingformaldehyde with approximately equivalent proportions of hydrochloricacid and an alkali metal salt of a dithiocarbamic acid, the reactionbeing. carried out at a temperature less than about C., at least one molof formaldehyde being present for each mol of the dithiocar bamate, thereaction product containing. nitrogen and sulfur in the same ratio athat in which they are present in the said dithiocarbamate.

2. As a new composition of matter, a product obtained by reactingformaldehyde .with approximately equivalent proportions of hydrochloricacid and an alkali metal salt of a dithiocarbamic acid derived from asecondary amine, the reaction being carried out at a temperature lessthan about 15 C., at least one mo] of formaldehyde being present foreach mol of the dithiocarbamate, the reaction product containingnitrogen and sulfur in the same ratio as that in which they are presentin the said dithiocarbamate.

3. As a new composition of matter, a product obtained by reactingformaldehyde with approximately equivalent proportions of hydrochloricacid and an alkali metal salt of a dithiocarbamic acid derived from asecondary aliphatic amine, the reaction being carried out at atemperature less than about 15 C., at least one mol of formaldehydebeing present for each mol of the dithiocarbamate, the reaction productcontaining nitrogen and sulfur in the same ratio as that in which theyare present in the said dithiocarbamate.

4. [As a new composition of matter, a product obtained by reactingformaldehyde with approximately equivalent proportions of hydrochloricacid and an alkali metal salt of a dithiocarbamic acid derived from adiaralkyl amine, the reaction being carried out at a temperature lessthan about 15 C., at least one mol of formaldehyde being present foreach mol of the dithiocarbamate, the reaction product containingnitrogen and sulfur in the same ratio as that in which they are presentin the said dithiocarbamate.

5. As a new composition of matter, a product obtained by reactingformaldehyde with approximately equivalent proportions of hydrochloricacid and an alkali metal salt of dimethyl dithiocarbamic acid, thereaction being carried out at a temperature less than about 15 C., atleast one mol of formaldehyde being present for each mol of thedithiocarbamate, the reaction product containing nitrogen and sulfur inthe sam ratio as that in which they are present in the saiddithiocarbamate.

6. As a new composition of matter, a product obtained by reactingformaldehyde with approximately equivalent proportions of hydrochloricacid and an alkali metal salt of dibenzyl dithiocarbamic acid, thereaction being carried out at a temperature less than about 15 0., atleast one mol of formaldehyde being present for each mol of thedithiocarbamate, the reaction product containing nitrogen and sulfur inthe same ratio as that in which they are present in the saiddithiocarbamate.

7. As a new composition of matter, a product obtained by reactingformaldehyde with approximately equivalent proportions of hydrochloricacid and an alkali metal salt of ditetrahydroalphafurfuryldithiocarbamic acid, the reaction being carried out at a temperatureless than about 15 C., at least one mol of formaldehyde being presentfor each mol of the dithiocarbamate, the reaction product containingnitrogen and sulfur in the same ratio as that in which they are presentin the said dithiocarbamate.

8. As a new composition of matter, a product obtained by reactingformaldehyde with approximately equivalent proportions of hydrochloricacid and an alkali metal salt of a dithiocarbamic acid derived from anamine having the structural formula HN/ \R in which R is a radicalselected from the group consisting of alkyl, alicyclic,tetrahydrofurfuryl, furfuryl and aralkyl groups and R is a radicalselected from the group consisting of alkyl, alicyclic,tetrahydrofurfuryl, furfuryl, aralkyl and aryl groups, the reactionbeing carried out at a temperature less than about 15 C., at least onemol of formaldehyde being present for each mol of the dithiocarbamate,the reaction product containing nitrogen and sulfur in the same ratio asthat in which they are present in the said dithiocarbamate. 1

9. A process which comprises'reacting formaldehyde with a freedithiocarbamic acid, at least one mol of formaldehyde being present foreach mol of the dithiocarbamic acid.

10. A process which comprises reacting formaldehyde with a freedithiocarbamic acid derived from a secondary amine, at least one mol offormaldehyde being present for each mol of the dithiocarbamic acid.

11. A process which comprises reacting formaldehyde with approximatelyequivalent proportions of an acidulating agent and a metal salt of adithiocarbamic acid, at least one mol of formaldehyde being present foreach mol of the dithiocarbamate, the reaction being carried out at atemperature at which the free dithiocarbamic acid liberated from thedithiocarbamate by the acidulating agent does not decomposebut reactswith the formaldehyde.

12. A process which comprises reacting formaldehyde with a mixture ofapproximately equivalent proportions of hydrochloric acid and an alkalimetal salt of a dithiocarbamic acid, the reaction being carried out atapproximately room temperature.

13. A process which comprises reacting formaldehyde with approximatelyequivalent proportions of an acidulating agent and a metal salt or adithiocarbamic acid derived from an amine having the structural formulain which R is a radical selected from the group consisting of alkyl,alicyclic, tetrahydrofurfuryl, furfuryl and aralkyl groups and R is aradical selected from the group consisting of alkyl, alicyclic,tetrahydrofurfuryl, furfuryl, aralkyl and aryl groups, at least one molof formaldehyde being present for each mol of the dithiocarbamate, thereaction being carried out at a temperature at which the freedithiocarbamic acid liberated from the dithiocarbamate by theacidulating agent does not decompose but reacts with the formaldehyde.

JOY G. LICHTY.

